This project examines effects of drug use and HIV infection on measures of cerebral function in specific regions of the frontal lobe; the effect of drug use on nueropshchological function across stages of HIV infection; examine the role of cognitive impairment, progression of HIV infection and psychiatric disorder on severity and duration of drug usage; examine the longitudinal effects of drug use and its interaction with stage of HIV ainfection on the nature of neuropsychological dysfunction, the rate of cognitive decline, and the changes in cerebral metabolism.